The aim of this research proposal is to understand the molecular events occurring during transformation by murine retroviruses. We propose to analyze in detail the role of various viral genes in the life cycle of murine retroviruses. Specifically, we plan to molecularly clone the unintegrated and integrated forms of several murine retroviral DNAs. The molecularly cloned DNAs will be used to prepare specific probes to study the mode of integration of viral DNA in the host chromosome. The biological activity of the cloned viral DNAs will be assayed and attempts will be made to generate deletion, insertion and site-specific mutants. The role of adjacent cellular sequences on the biological infectivity of the viral DNAs will be studied. We also plan to study the biogenesis of Moloney mouse sarcoma virus specific mRNAs. Using specific probes we plan to study the expression of M-MSV src specific sequences in uninfected cells. The molecularly cloned viral DNA will be used as template for in vitro transcription in a soluble DNA dependent RNA polymerase II system. Finally, we propose to construct retroviral DNAs as eukaryotic cloning vectors.